The present invention is directed to piezoelectric crystal resonators and, more specifically, to the shape, size and cutting angle of a piezoelectric crystal resonator vibrating in a width-extensional mode.
A NS-GT cut coupling quartz crystal resonator which vibrates in the coupled width-extensional mode and length-extensional mode is well known and used as a time standard of consumer products and communication equipment. FIG. 17 shows a plan view of the conventional NS-GT cut coupling quartz crystal resonator. In FIG. 17, The resonator 200 comprises vibrational portion 201, connecting portions 203, 206 and supporting portions 204, 207. The supporting portions 204 and 207 include respective mounting portions 205 and 208.
In addition, as shown in FIGS. 17 and 18, electrodes 202 and 211 are disposed on the upper and lower surfaces of the vibrational portion 201, the electrode 202 extends to the mounting portion 205 through the connecting portion 203, while the electrode 211 extends to the mounting portion 208 through the connecting portion 206. The electrodes 202 and 211 have opposite electrical polarities, and two electrode terminals are constructed. Also, the resonator is mounted on lead wires or a pedestal by adhesives or solder at the mounting portions 205 and 208.
When an alternating voltage is applied between both electrodes 202 and 211, and electric field Et occurs alternately in the thickness T direction, as shown by arrow signs of the solid and broken lines in FIG. 18. As a result, the width-extensional mode and the length-extensional mode whose frequencies are inversely proportional to width W and length L of the vibrational portion, respectively, can be excited at the same time, and the NS-GT cut coupling resonator coupled in inverse phase is provided. The above-mentioned resonator is formed integratedly by a chemical etching process.
In addition, the lager the area of vibrational portion for the NS-GT cut resonator becomes (low frequency), the smaller series resistance R1 becomes and the larger quality factor Q becomes. Also, the NS-GT cut resonator with excellent frequency temperature behavior is determined by a dimensional ratio W/L, and which has a value of 0.95 approximately. In order to get a higher frequency, it is necessary to decrease the area of the vibrational portion for the resonator.
Recently, according to the miniaturization and weight lightness of consumer products and communication equipment with a frequency higher than 3.5 MHz, a miniature NS-GT cut resonator with the frequency is also required with a small series resistance R1 and high quality factor Q.
It is, however, impossible to provide a miniature NS-GT cut resonator with a frequency higher than about 3.5 MHz with a small series resistance R1 and a high quality factor Q because the area of vibrational portion for the resonator becomes very small to get a higher frequency, and more an electro-mechanical transformation efficiency becomes small, so that series resistance R1 becomes large and a quality factor Q becomes small.
It is, therefore, desirable to provide a novel and miniature quartz crystal resonator with a frequency higher than about 3.5 MHz with a small series resistance R1, a high quality factor Q and excellent frequency temperature behavior over a wide temperature range.
The present invention relates to a width-extensional mode piezoelectric crystal resonator vibrating in the single mode with a high electro-mechanical transformation efficiency and relates to cut angle, electrode construction and resonator shape thereof.
In particular, the present invention relates to the width-extensional mode piezoelectric crystal resonator with a new cut angle and new electrode construction which is available for wearable equipment, communication equipment, measurement apparatus and consumer products employing quartz crystal or lithium tantalate (LiTaO3) or lithium niobate (LiNbO3) as a piezoelectric material and requiring miniaturization, high accuracy, shock-proof and low prices for the crystal resonator.
It is an object of the present invention to provide a width-extensional mode piezoelectric crystal resonator with a high electro-mechanical transformation efficiency.
It is an another object of the present invention to provide a miniature width-extensional mode piezoelectric crystal resonator with a frequency higher than about 3.5 MHz with a small series resistance R1 and a high quality factor Q.
It is a further object of the present invention to provide a width-extensional mode piezoelectric crystal resonator with good frequency temperature behavior over a wide temperature range.
In order to accomplish a miniature width-extensional mode piezoelectric crystal resonator with a frequency higher than about 3.5 MHz with a high electro-mechanical transformation efficiency which gives a small series resistance R1 and a high quality factor Q, it is necessary to provide a width-extensional mode piezoelectric crystal resonator which is formed from a piezoelectric crystal plate with the new cut angle, the new electrode construction and a large piezoelectric constant.
In accordance with the present invention, this is accomplished by new cut angle and having new electrode construction and a large piezoelectric constant.
In full detail, such a resonator is formed in accordance with the present invention, from a piezoelectric crystal plate of new cut angle.
Moreover, such a resonator is provided in accordance with the present invention, by new electrode construction and large piezoelectric constants.
In addition, in accordance with the present invention, an improvement of frequency temperature behavior for a width-extensional mode piezoelectric crystal resonator is accomplished at least by two resonators connected and formed integratedly through frame or supporting frame. The crystal resonators with each different turn over temperature point Tp are electrically connected in parallel. As a result of which, the integratedly formed crystal resonator of the present invention has good frequency temperature behavior over a wide temperature range.
The present invention will be more fully understood by referring to the following detailed specification and claims taken in connection with the appended drawings.